Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices or as an auxiliary power unit. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (Plug-In HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle or large-sized devices, such as vehicles, or an auxiliary power unit uses a middle or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle or large-sized devices or the auxiliary power unit.
Preferably, the battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell (unit cell) of the middle or large-sized battery module. In particular, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
Generally, a plurality of battery cells is stacked and fixed using long bolts to constitute a battery module. However, the thickness of portions of the battery module at which the long bolts are fastened is less than that of the other portions of the battery module with the result that it is difficult to maintain dimensional stability.
Also, dimensional stability of the battery module may not be maintained due to accumulated tolerance generated at welded portions between electrode tabs and bicells of each of the battery cells.
The battery module may be individually used. Alternatively, two or more battery modules may be combined to constitute a battery pack. In this case, if dimensional stability of the battery pack is not maintained, the battery modules are not fixed in the battery pack when strong external impact or vibration is applied to the battery pack with the result that durability or safety of the battery pack is lowered.
If dimensional stability of the battery pack is maintained, the battery pack may be configured based on dimensions such that the battery pack is protected from strong external impact or vibration, thereby improving durability or safety of the battery pack.
Consequently, there is a high necessity for a battery module having a novel assembly structure to solve the above problems.